1. Field of the Invention
This invention relates to organopolysiloxane compositions and, more particularly, to such compositions that can be cured to produce pressure-sensitive adhesives.
2. Description of the Prior Art
Silicone-based pressure-sensitive adhesives are well known and are commonly prepared by blending copolymeric resins containing triorganosiloxy units and SiO.sub.4/2 units with silanol endblocked polydiorganosiloxanes, such as taught in U.S. Pat. Nos. 2,736,721, 2,814,601, and 2,857,356.
More recently, organopolysiloxane compositions that are prepared by reacting organopolysiloxanes containing olefinic unsaturation with organopolysiloxanes containing silicon-bonded hydrogen in the presence of a hydrosilation catalyst have been developed for use as molding resins, elastomers, release surfaces, and adhesives. See, for example, U.S. Pat. Nos. 3,699,073, 4,208,504, 4,248,750, and 4,386,135.
The use of a substantially linear diorganohydrogensiloxy endblocked polydiorganosiloxane in combination with a substantially linear diorganovinylsiloxy endblocked polydiorganosiloxane to simulate a high molecular weight polydiorganosiloxane gum while maintaining a low viscosity has been described. See, for example, U.S. Pat. Nos. 3,699,073, 4,340,709, 4,426,240, and 4,535,141.
The curing of silicone-based adhesive compositions by means of a hydrosilation reaction has also been disclosed. See, for example, U.S. Pat. Nos. 3,983,298, 4,051,454, and 4,774,297.
While the hydrosilation reaction of alkenylsiloxanes with hydrosilanes in the presence of a suitable catalyst has been used to prepare potting, molding, and elastomeric products as well as materials useful for providing substrates with a release surface, the reaction has been used only to a limited extent to provide pressure-sensitive adhesives.